Stochastic Trends in Global Sea Level Rise

Wednesday, 17 December 2014
Victor Ocana1, Eduardo Zorita2 and Patrick Heimbach1, (1)Massachusetts Institute of Technology, Cambridge, MA, United States, (2)Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research, Geesthacht, Germany
Global mean sea level (GMSL) has been rising since (at least) the 19th century and the rate of rise may be increasing. Several studies that attempt to explain variability of GMSL during the instrumental record share the common assumption that GMSL variability is deterministic in nature and different from natural variations. Here we show that GMSL variability can alternatively be explained, at least in part, as being caused by random variations and hence not having a deterministic origin. This internal variability, which adds to externally forced changes (e.g. through anthropogenic climate change), is a consequence of the integrated character of GMSL, which is the cumulative addition of temporal contributions that exhibit random character, and whose integration results in GMSL variations with persistence on decadal-centennial time scales. The generation of variability by integration of random stationary noise (i.e. even in a constant climate) is a robust and fundamental feature of stochastically forced systems with memory. The integrated character of GMSL results in an intrinsic difficulty in distinguishing internal from externally forced variations.